The invention relates to improvements in methods of and in apparatus for the application of adhesive spots or patches to intermittently transported objects, such as a series of successive blanks of paper, cardboard, plastic or the like. More particularly, the invention relates to improvements in methods of and in apparatus for applying (e.g., by one or more nozzles or analogous implements) spots or patches of adhesive to a succession of objects which are being advanced in stepwise fashion and in accordance with a predetermined pattern, preferably as regards the extent, the frequency and/or the rate of movement of successive objects along a predetermined path. Examples of objects which are being advanced or transported in the above outlined manner are blanks which are utilized in the tobacco processing industry for conversion into packs or other types of receptacles for smokers' products, e.g., for arrays of plain or filter cigarettes, cigars, cigarillos or analogous rod-shaped products.
It is customary to employ valve-controlled nozzles in pasters which serve to apply (preferably or desirably) equal quantities of a suitable adhesive in various types of machines which are utilized in the tobacco processing industry. Patches, spots or continuous or interrupted strips of a suitable adhesive can be utilized for the making of longitudinal seams including the overlapping marginal portions of converted webs (envelopes or wrappers) of cigarette paper, tipping paper or the like. Those parts which are utilized to initiate or terminate the application of an adhesive to successive blanks of cigarette paper or the like (such parts can include, for example, mobile constituents of valves and/or valve-controlled nozzles) are invariably influenced by inertia which must be taken into consideration if the application of adhesive spots is to take place with a required or desired degree of predictability, uniformity and reproducibility. In other words, it is desirable and necessary to include, into the calculation of intervals during which a nozzle is to actually discharge adhesive from a suitable source onto successive objects of a series of successive objects, the intervals of succesive alternating accelerations and decelerations of the conveyor system for the series of objects as well as the intervals which elapse between successive assumptions by the valve or valves of its or their fully open and fully closed positions.
When the application of an adhesive is to take place in certain branches of the tobacco processing industry, the accuracy and predictability of such application are greatly influenced by the continuously increasing frequency at which the objects which are to receive spots or patches of adhesive must be advanced toward, past and beyond one or more adhesive applying stations. For example, patches of adhesive must be applied to selected portions of blanks which are to be converted into so-called soft or hinged-lid packs for arrays of cigarettes or the like. The patches must be applied to various tucks and/or flaps and/or panels and/or lids and/or walls in order to ensure that each adhesive-coated part will reliably adhere to a neighboring part when the conversion of a blank into a packet confining an array of cigarettes or the like is completed.
Presently known proposals to compensate for inertia of moving parts in the conveyor system and/or in the adhesive applying system for a series of objects (such as blanks of paper, cardboard or the like and hereinafter called blanks for short) include the resort to a preliminary or advance regulation. Such regulation takes into consideration certain specific values which are characteristic of moving parts (e.g., in a valve) and of their inertia in dependency upon various parameters, such as the nature and consistency of the adhesive, the pressure, the temperature and/or certain other variables. This is intended to ensure that, if the rate of transport of the blanks is at least substantially constant, the dimensions, the shapes and the locations of successively applied adhesive spots will at least approximate the desired values.
It has been ascertained that the presently known proposals to accurately meter the application of adhesive under the above outlined circumstances are often unsatisfactory, especially when accurately defined spots containing predetermined (optimum) quantities of a selected adhesive (e.g., a pasty adhesive) are to be applied to intermittently advanced blanks which are repeatedly accelerated, moved at full speed and thereupon decelerated at a high frequency, e.g., as required in a modern high-speed cigarette packing machine.